On Mon, 22 Sep 2003 13:09:54 -0700, Jim Thompson
wrote:

I have a 1086-1094MHz monopole (rubber-ducky) antenna mounted
(vertically/BNC connector thru circular ground-plane).

I would like to modify the ground plane so that it sees only signals
in a cone from 45° above horizon and upwards.

I'm clueless in this antenna world.

How should I do this?

Thanks!

...Jim Thompson

Hi Jim,

Leave ground alone and make the antenna longer. Roughly 7 cM is
quarterwave (probably the size of your current antenna). Or twice
that for a halfwave. You want to maintain an integral multiple of
either to make it at least one wavelength tall. If it is 7 cM, then
try 21 or 35 cM (using odd, integral multipliers). If it is 14 cM,
then try 28 or 42 cM (using even, integral multipliers).

The reason is that longer antennas become end-fire (that is, oriented
along their length instead of broadside). The odd/even distinction is
to maintain the expected load which repeats in these multipliers.

73's
Richard Clark, KB7QHC